In a toroidal reactor utilizing ohmic heating coils that are constantly energized, flowing coolant must be distributed to the various turns of the ohmic heating coil in order to remove the joule heat generated. In prior art tokamak fusion reactors (TFR), the devices were experimental and large enough that OH coil flow distribution problems seldom arose. There was sufficient space in the vicinity of coolant inlets and coolant outlets to control the static pressure rise and the static pressure drops respectively and the cooling requirements were such that adequate coolant flow could be attained with little regard to the coolant flow path through the ohmic heating coils per se. In commonly assigned U.S. Pat. No. 4,367,193 filed Oct. 22, 1979, and U.S. Pat. No. 4,363,775 filed June 10, 1980, there is disclosed a compact TFR with the central ohmic heating (OH) coil disposed in the very limited space surrounding the main axis of the TFR and inside of the toroidal field (TF) turns. Because of the limited space available for the OH coil coolant manifold between the OH and TF coils, a high pressure loss results in this manifold. This high pressure loss makes it difficult to achieve a good distribution of coolant flow to the various turns of the OH coil, and other poloidal field (PF) coils, even where the inlet manifold configuration is designed to offset to the greatest extent possible the outlet manifold effects.
In addition, owing to the temperature gradient existing in the OH and other PF coils, there exists a need to create a specific temperature profile in the coils so that proper coil resistivity is maintained.
Because of the density and the distribution of the current flow in the OH and PF coils of a compact TFR, there is a need to dissipate very high amounts of heat in a very small space and preferably in an unequal manner. The density is non-uniform, being greater at the smaller radii, thus producing non-uniform, non-optimum hoop stress, with the smallest radius being the most highly stressed.